Cover the beets with cold water in a heavy saucepan and boil until fork tender, about 1 1/2 hours. Drain them in a colander and let them cool just until you can handle them. Peel them warm (the skin slides right off if they're warm), then cut them into 3/4-inch cubes. You should have about 3 cups.,______,In large flameproof casserole, whisk together the turmeric, flour, sugar, mustard, and 1 cup of the vinegar to make a paste. Add the remaining 3 cups of vinegar and whisk until smooth. Over medium heat, bring the sauce to a boil and cook until it thickens, about 3 minutes, whisking continually to keep lumps from forming. Add the vegetables, stirring to coat them, and cook for 5 minutes. Remove from the heat and allow the mixture to cool to room temperature.,Refrigerate the piccalilli for up to 2 weeks.